Tuesday 26 September 2023

Diy Gatr Ball Antenna for QO100

I wanted to see if i could make a working version of the Gatr ball antenna typically used for geostationary satellites, it is often seen at military sales shows and at fancy trade shows, i heard these types of antenna sell for $150,000? Well I thought surely i could do it myself.

I have been making fabric parabolic antennas for a number of years now. 

They work really well, I am regularly receiving HRPT and QO100 satellites via software defined radio using this method. Have a look at my ebay listings if you are interested in one. its super lightweight and portable allowing me to receive HRPT satellites one-handed using only a mobile phone.

Anyway I figured why limit myself to this parabola type of antenna, why not try new possibilities. So I have always been interested in the cool looking Gatr ball antenna but because it is difficult to see inside and understand how it works how would it be possible to know what is inside making it all tick. 

It was after seeing this image showing the dish that I thought I should give it a chance and see if the fabric for my folding parabolic antenna will work in this scenario.

So i bought myself a nice big beachball, hacked it open and stuck a fabric reflector inside. here was the resulting prototype number 1:

Here you can clearly see a fabric reflector inside and a LNB receiver on the exterior. I used this to test receive QO100 voice signals. To stretch out the reflector i used a number of elastic anchor supports i made and glued inside. Once I had it all fixed in there I closed it up and sealed it so I could inflate the ball.

So onwards I go to a bigger larger version:

This one worked much better. the ball radius was significantly larger than my first one and this improved the receiving signal to a level i could confidently listen to QO100 voice.

 Here we can see an example of QO100 reception using the XL ball antenna i built. It works excellently for a beachball ;) I attached tethering lines and weights to secure my antenna in place as the satellite is stationary and not orbiting so i do not have to worry about tracking it.

Transmitting is also possible. I 3D printed a combined tx/rx helical feed/LNB and using Adalm pluto SDR with a power amplifier i was able to transmit test signal. 

Overall I am happy with my setup. I achieved my goal of receiving a satellite with a homemade Gatr antenna, and I feel that this was a sucessful experiment. 


Further experiments are also possible using the fabric antenna method such as nasa's rovers using UHF collapsible fabric antenna which uses a quadrifiliar helical format. Here on earth we could make LRPT fabric folding helical just like QFH antenna.

If you would like me to make you one please get in touch via my ebay page in the links above.

Thanks for reading.

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